Insulating column structure



breakdown and flashover.

Patented May 23, 1950 2,509,009 INSULATING COLUMN STRUCTURE Joseph L. McKibben, Los Alamos, N. Mex, as signor to the United States of America as repre-' sented by the United States Atomic Energy Commission Application October 8, 1948, Serial No. 53,401

(Cl. zen-27.5)

(ll-aims.

The present invention relates to high voltage apparatus and, more particularly, to insulating structures employed to separate bodies at widely different potentials in such apparatus.

In many applications of high voltage apparatus or systems, it has been found that the overall effectiveness is limited by the resistance of the insulating structures to spark over or discharge breakdown. Many attempts to maximize this resistance to breakdown for well known insulating materials such as glass, porcelain or the like, have been described in the literature and are well known. For example, it has been found that structures comprising a plurality of non-conducting sections separated by metallic shims or the like have been able to withstand higher potential difierences than a solid or laminated structure of the same insulating material not separated by the equipotential shims. Such a structure is described in the U. S. patent to Machlett et al., No. 2,376,439 issued May 22, 1945.

While such laminar structures have been found somewhat efiective in normal high voltage applications, in apparatus in which the potential difierence between operating electrodes is of the order of many hundreds of kilovolts, cold emitted electrons following the electric field have led to Thus, while the insertion of equipotential shims or devices serving a similar purpose between sections of insulating material have been found to equalize the potential stress applied to the insulating material, they have not prevented cold emission induced breakdown and in fact have contributed to such breakdown to some extent in the voltage range being considered. Furthermore, the elongation of surface creepage paths as disclosed by Trump in U. S. Patent 2,182,185 does not avoid the breakdown induced by cold emitted electrons in the same range.

It is thus seen to be an object of the present invention to provide improved high voltage apparatus capable of operating at maximized potential difierence between the principal electrodes while minimizing the spatial separation of said electrodes.

It is a further and more specific object of the present invention to provide an insulating structure for separating bodies operating at high potential difierences which is extremely simple to construct.

Another object of the present invention is to provide an insulating structure which minimizes breakdown or flashover due to cold emission of electrons by the materials employed in the structure.

Other objects and advantages will be apparent to one skilled in the art from the following description when taken'in connection with the drawings made part of this specification.

In the drawings:

Figure 1 is a longitudinal sectional view of high voltage apparatus embodying one form of the invention.

Figure 2 is a similar section in enlarged view 0 a portion of the apparatus shown in Figure 1 and providing details of the insulating structure.

Referring now to the drawings, the apparatus shown in Figure 1 is seen to comprise an elongated tubular envelope ill of suitable insulating material such as a glass composition, a pair 01' operating electrodes H and I2 supported in spaced relationship by end pieces l3 and 14 respectively and a source of direct current potential l5 associated with said electrodes and adapted to apply a direct current potential of the order of twelve to fifteen million volts between the same. The entire envelope H1 is hermetically sealed and adapted to withstand an external pressure oi upward or p. s. i. and to be internally evacuated, for example, to the extent that the residual pressure is approximately of the order of 10' millimeters of mercury or less.

Electrode I l is adapted to permit the introduction into the evacuated tube of ions or a predetermined type, for example, deuterons, the type 01' source and manner of introduction being indicated schematically and generically referred to by numeral l6 as the details thereof are well known in the art and form no part of the present invention.

Electrode 12, on the other hand, is adapted to act as a target for the ions introduced at electrode H and accelerated in a beam by the twelve million volt potential diiierence established be tween said electrodes II and l2.

NOW in such a device, iiprinciples heretofore known were followed, the spatial separation of electrodes l I and I2 would be great and dispersion of the charged particle beam would occur necessitating the introduction of a plurality or focussing electrodes and otherwise complicating the structure. In the present apparatus, it is possible to separate the electrodes by less than twelve feet, the insulating structure of envelope 10 being capable of operating under a potential difierence of over 1,000,000 volts per foot.

The details of envelope I0 of the insulating structure are shown in Figure 2. It is seen to be constructed of a plurality of annular rings 20 of insulating material, separated by conducting annular shims 2|. Rings 20 have parallel flat or plane faces which are perpendicular to the axis thereof. Sealing is accomplished by the application to adjacent plane faces of the shims 2! and rings 20 of a suitable cementitlous material such as, for example, a vinyl plastic composition or the like. It has been found highly desirable in cementing the structural parts together to carefully clean the resulting joints and the surrounding materials'with suitable solvents.

It is a feature of the present invention that the annular sections zli are provided with a taper in the internal borethereof, the direction of the taper being such that the diameter of the bore at the more ositive plane surface (indicated by the plus sign) is larger than the diameter of the bore at the less positive plane surface (indicated by the minus sign).

It is immediately apparent that the-cold emission of electrons under the influence of the intense electric field which exists, inthe axialdr rection is substantially ineffective to cause breakdown or fiashover of the insulating material. More particularly, if 'cold emitted electrons are emitted at point A they follow the direction of the electric field: i: e-., a path perpendicular to the plane surface or the ring 2ll are parallel to the longitudinal axis, and are thus led away-irom the said insulating-material and cannot bombard the sameto ultimatelycause electrical breakdownthereof.

The taperis preferably uniform and about fifteendeg-rees to the axis, the exact taper beinggoverned to some extentby the insulating materialemplcyed; The taper-should be at least suchas to prevent the saidcold emitted electrons-from following a pathwhich leads-to any portion-oi=ring205-thus-indicating that it is not the increased creepage-pathefiorded by the taper, but rather the interrelation of the electric field direction and the insulating material surface which leads to the desirable results hereinv disclosed;

It is thus: seen that what has been described herein. for the purpose of: illustration, is a single embodiment throughwhich. the principles ot the invention may be carried out. While'theinner bore of the insulating-material section in the embodiment described is preferably uniformly tapered, motherapplications thetaper'may well vary, the essential principle being that cold emittedelectrons are prevented by the angular relation between the surfacaof: the. bore and the electric field, from. returning to. the said. surface.

Likewise, itisapparent that/many othervariations in structure and materials; will suggest themselves. to one skilledin' thear-t, however, such variations should be deemed to fall within the scope of the inventiontasit is: definedwith particularity in the appended :claims.

What is-iclaimed is:

1. combination with at lea-st onelpair-o'f operating electrodes, a source of -direct current .potentialland means-for connecting said source to saidelectrodes to-establishahighipotentialzand an. electric field-therebetween of. an insulating structure forsupporting said electrodes infixed spaced relationship; comprising a plurality of annular. sections of insulating 1 material disposed in axial alignment, annular-conducting. shims separating-said insulating material. sections. and

ment with-said electric field, the-"diameter of said bore at-the more positive plane surface oi said annular sections islarger-than the diameter of said boreat-the less positiveplane-surface of said sections.

2: A tubularinsulating structure-which comprisesia plurality. o-f.- annular sections: of. insulatmgematerial'axially aligned and separated by an nular conducting shims, the inner bore 0! said insulating material sectionsbeing tapered in such a ma ner t a when said se ions are sp sed in substantial axial alignment with an electrical field, the diameter of said boreat the more positive face ofeach of said sections is greater than thediameter of, said bore at the less positive face of the samesection.

3. A tubular insulating structure which comprises a pluralityof annular sections of insulating material saidv sections having parallel plane faces and being axially aligned and separated by annular conducting shims, the inner bore of said insulating material sections being uniformly tapereciin such a manner that when. said. sections are disposed in. substantial: axial alignment. with an electrical field, the diameter oi: said. bore-at the more positive; face-of? eachotsaid sections; is greater than thediameter of; said iboreat the less positive face of the same section.

41. An insulating; envelopeior supp lltingzat least two bodies ata high. potential difference is spaced relationship comprising; a. pair; of; closure sections each. adaptedtto support at. least. one. of said bodies, aiplurality. of. plane facedannular insulating. sections disposed. between. said closure sections, said. insulatin sec ions being. axially aligned. and. separated by conducting1 material shims, said. shims havin their plans.- faces; sealed to .adiaccnt.fa.ces.zoi saidinsulating sections and s id. closure sectionspb ins. sealed. '00.. t e. insulatin sections. adjacent, thereta. at. least th inner boreiof. ach. of s id. in la in ection being taper d.insuchama nenthat wh n sa d ect o are disposed in substantial axialcalignment with electrical. fieldth diamet o Said. on at the more positive face of each of. saidsectionsis greater, than the diameter of said bore at the, less positive face ofthe same section.

5. An insulating envelope for supporting at least two bodies ata high potentialdifference in spacedrelationship comprising a pair, of. closure sections each adapted to support, at least one of said bodies, a plurality of planefaced annular insulating sections. disposed between said closure sections, said'insulating sections being axially. aligned and separated by conducting material shims, said shims'havingtheir plane faces sealed to adjacent faces of 's'aidinsulating sections and saidclo'sure section being sealed to the insulating sections adjacent thereto, at'least' the inner bore of" each oi'saidiin'sulating sections being uniformly tapered in such a manner that when said sections are disposed in substantial" axial alignmentwith an electrical field, the diameter of said bore at'the more positive face ofeach'ofsaid sections-is greater than t-he diameter of-said bore at the less'positivefac'e oi-=the-samesection;

JOSEPHL. McKIBBEN; 

